The objective of this proposal is to determine how chemokines and newly identified chemokine antagonists, Slits, are regulated, interact with each other, and contribute to inflammation in response to renal injuries. Past research in chernokines has been focused mostly on positive regulation. Thus, in all these situations chemokines are invariably studied as activators or attractants. Recently, we have found that one of the neural axon guidance cues, Slits, was expressed outside of the nervous system, Slit-2 was expressed in the kidney and lung. Leukocytes have been considered as early and important effectors in renal inflammation. Previous studies have shown upregulation of chemokines and downregulation of Slit2 during glomerulonephritis and Slit treatment significantly attenuated nephritic injury. It was reported that Slit/Robe may function through Robe's binding to GTPase activating proteins (GAPs, srGAPs) Recently, we have found that Racl and Cdc42, small GTP binding proteins known for their roles in actin polymerization and cell motility, were shown to be negatively regulated in macrophage-like cells by Slit2. We plan to study the expression and regulation of chemokines, Slits, and Robe in the model of renal ischemia/reperfusion and further determine the role of Slit/Robe in negative regulation of leukocyte accumulation in this model. Another goal of this project is to characterize Slit/Robe mediated signaling of small G proteins in leukocytes. Differences between activation of GTPases between neurons and leukocyte suggests that Slit/Robe in ieukocytes may use other signaling molecules in addition to srGAPs, therefore, we plan to further clone Robe-interacting proteins in mononuclear cells by Two-Hybrid System. The proposed studies will shed new light on how chemokines and Slit interact in leukocyte-dependent renal injury, and uncover the signaling pathway of Slit/Robo, and insights gained from our study will lead to the development of new therapeutic strategies of chemokine-dependent renal injuries in human.